Salve!
il mio codice non ha errori sintattici, ma quando lo mando in esecuzione mi visualizza questo messaggio:
codice:
Exception in thread "main" java.io.InvalidClassException: Appuntamento; local cl
ass incompatible: stream classdesc serialVersionUID = 3940645796886402842, local
 class serialVersionUID = -3537395523583988341
        at java.io.ObjectStreamClass.initNonProxy(ObjectStreamClass.java:562)
        at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:158
3)
        at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1496)
        at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1
732)
        at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1329)
        at java.io.ObjectInputStream.readObject(ObjectInputStream.java:351)
        at java.util.ArrayList.readObject(ArrayList.java:593)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.
java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAcces
sorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:974
)
        at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1846)

        at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1
753)
        at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1329)
        at java.io.ObjectInputStream.readObject(ObjectInputStream.java:351)
        at Agenda.readfileobj(Agenda.java:39)
        at InterfacciaAgenda.gestfile(InterfacciaAgenda.java:27)
        at ApplicazioneAgenda.main(ApplicazioneAgenda.java:21)
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